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# MCAT Chem

### Ch. 8 DC and AC Circuits

Question | Answer |
---|---|

current | movement of charge between two points that exist at different electrical potentials. movement of positive charge to higher potential (positive) to lower potential (negative) |

Kirchhoff's first law | the first law states that the sum of currents directed into a point within a circuit equals the sum of the currents directed away from that point |

Kirchhoff's seconds law | the sum of the voltage sources is equal to the sum of the voltage drops around a closed loop circuit |

resistance | the opposition to the movement of electrons through a material |

conductors | materials that have low resistance |

resistors | conductive materials that have moderate resistance |

insulators | materials that have very high resistance. |

what is resistance related too | the resistivity and is proportional to length of the resistor and inversely proportional to the cross-sectional area of the resistor |

ohm's law | for a given resistance, the voltage drop across a resistor is proportional to the magnitude of the current through the resistor |

resistors in series | additive to give a resultant resistance that is the sum of all the individual resistances. |

resistors in parallel | the magnitude of the current through each circuit division will be inversely proportional to the magnitude of the individual resistances of each circuit division |

capacitor | when two electrically neutral metal plates are connected to a voltage source, positive charge builds up on plate connected to positive (higher V) terminal, negative charge builds up on plate connected to negative (lower V) terminal. |

when will charge collect on the plates of a capacitor | any time there is a potential difference between the two plates. |

capacitance | the ratio of the magnitude of the charge stored on one plate (abs val. of charge) to the total potential difference, voltage, across the capacitor. C=Q/V |

SI unit for capacitance | farad. 1F = 1 coulomb/volt |

capacitance dependent on geometry | C=e.(A/d) e.=epsilon knot=the permittivity of free space 8.85X10^-12 F/m, A=area of overlap of two plates, d=distance between two plates. |

magnitude of electric field between plates | E=V/d. direction will point away from positive plate toward negative plate |

potential energy stored in a capacitor | U=1/2CV^2 |

dielectric material | fancy way of saying insulation. when insulating (air, glass, plastic, ceramics, metal oxides) is placed between charged capacitor, the voltage across the capacitor decreases |

what does placing a dielectric between the plates cause | voltage decrease caused by shielding the opposite charges from one another. because they feel each other less, V decreases. |

Equation for increase in capacitance due to dielectric effect | C'=KC where K=dielectric constant |

what does lowering the voltage between the plates due | makes room for more charge. charge is released from their holding plates either by discharging across the plates of through some conductive material |

difference between alternating and direct current | direct current flows in one direction only, while alternating current reverses direction periodically |

oscillation equation for AC | i=ImaxSin(2pift)=ImaxSin(wt) i=instantaneous current at time t, Imax=maximum current, f=frequency, w=angular frequency (w=2pif) |

RMS current and voltage equations | Irms=(Imax)/(2^(1/2)) Vrms=(Vmax)/(2^(1/2)) |

equations for power | P=IV, P=I^2R P=V^2/R |

resistivity | intrinsic resistance to current flow in a material. resistivity is the proportionality constant that relates a conductor's resistance (R) to the ration of its cross-sectional area (A) to the length of the resistor (L) R=(rhoL)/(A) |

resistance and temperature | most conductors have higher R at higher temps. increased thermal oscillation of atoms in conductive material produces a greater resistance to electron flow. temp is intrinsic quality of all matter, so think of resistivity is function of temperature |

Created by:
adam87
on 2010-07-12